Semiconductor element for switching purposes

ABSTRACT

A semiconductor device comprises a semiconductor element divided transversely into at least four zones which alternate in conductivity type. A control electrode is applied to a neighboring inner zone where this zone reaches to the outer surface of one of the outer zones through a perforation in the latter and metallizing is applied to this same surface but set back from the control electrode. The same outer zone has other perforations distributed therein and the neighboring inner zone extends as far as the metallizing. The perforations in the region of the vicinity of the control electrode are connected to the metallizing by a ring-shaped metallic layer which serves to short circuit the neighboring inner zone to the outer zone and also, upon a flow of anode current after firing, due to its relatively high resistance establishes a voltage drop sufficient for firing to spread rapidly at least regionally across the region of the outer zone not covered by metallizing.

United States Patent [151 3,638,080 Muller et a]. 1 Jan. 25, 1972 [54] SEMICONDUCTOR ELEMENT FOR Primary Examiner-Jerry D. Craig SWITCHING PURPOSES [72] Inventors: Elmar Muller, Alzey; Klaus Weimann,

Lampertheim, both of Germany [73] Assignee: Aktiengesellschaft Brown Boveri & Cie,

Baden, Switzerland [22] Filed: Feb. 17,1970

[21] App]. No.: 11,959

Related U.S. Application Data [63] Continuation-impart of Ser. No. 640,729, May 23,

1967, Pat. No. 3,531,697.

[30] Foreign Application Priority Data July 2, 1966 Germany ..B 87825 [52] US. Cl. ..3l7/235 R, 317/235 AB, 317/235 AB [51] Int. Cl. ..l-l0ll 11/10 [58] Field of Search ..317/235 [56] References Cited FOREIGN PATENTS OR APPLICATIONS 1,166,940 4/1964 Germany ..3l7/235 AtlameyPierce, Scheffler & Parker [57] ABSTRACT A semiconductor device comprises a semiconductor element divided transversely into at least four zones which alternate in conductivity type. A control electrode is applied to a neighboring inner zone where this zone reaches to the outer surface of one of the outer zones through a perforation in the latter and metallizing is applied to this same surface but set back from the control electrode. The same outer zone has other perforations distributed therein and the neighboring inner zone extends as far as the metallizing. The perforations in the region of the vicinity of the control electrode are connected to the metallizing by a ring-shaped metallic layer which serves to short circuit the neighboring inner zone to the outer zone and also, upon a flow of anode current after firing, due to its relatively high resistance establishes a voltage drop sufficient for firing to spread rapidly at least regionally across the region of the outer zone not covered by metallizing.

1 Claims, 2 Drawing Figures SEMICONDUCTOR ELEMENT son swrrcn no PURPOSES This application is a continuation-in-part of my copending application Ser. No. 640,729, filed May 23, 1967, now US. Pat. No. 3,531,697 granted Sept. 29, 1970.

This invention .relates to a semiconductor element for switching purposes provided with at least four zones of alternating types of conductivity; at least one control electrode, surface metallizing on the mutually opposing surfaces of the two outer zones, the metallizing on one outer zone not being disposed in the region in the vicinity of the control electrode, and a plurality of perforations which are distributed in the lastnamed zone, and in which the neighboring inner zone extends as far as the metallizing.

There is already a known semiconductor element for switching purposes wherein the metallizing on one outer zone is not disposed in the region in the vicinity of'the control electrode. This measure-which is also called a transverse-field emitter-causes the anode current toset up across the non contacted part of the outer .zone a voltage drop which causes firing to spread at relatively high velocity. The semiconductor element can thus tolerate relatively rapid increases of current without destruction. In order that the voltage drop across the noncontacted outer zonethe emitter-may attain a sufficient magnitude, the width of the noncontacted emitter surface beside the control electrode must not be less than a certain amount. In this connection reference is made to the article in the publication Applied Physics, Vol. 19 pp. 396, 1965.

There are, furthermore, already known semiconductor ele- According to an advantageous development of the invention, the perforations in the vicinity of the control electrode are connected by a layer of metal to the remaining metallizing on the emitter. The thickness-andthus the resistanceof this metal coating must be made such that, on the one hand, the inner zone is short circuited to the outer zone, but that .on the other hand, when anode current flows after firing, a voltage drop which is suflicient for firing to spread rapidly in a radially outward direction is set up across the region of the outer zone not covered by the metallizing. 1 r

Reference will now be made to the accompanying drawings, wherein one suitable embodiment of a semiconductor element in accordance with the invention is illustrated.

FIG. 1 shows a section through an embodiment of a semiconductor element, the perforations inthe vicinity of the control electrode being connected by a layer of metal to the remaining metallizing on the emitter, and r FIG. 2 shows a plan view of the semiconductor element ac-v cordingto'FlG. l. v v The semiconductor element according to FIG. 1 in the form of a wafer of silicon has four zones of alternating types of conductivity, one outer zoneth e emitter 1-with n conductivity,

the neighboring inner zone-the baseZ-with p conductivity,

a further base 3 with n conductivity, and the other outer zone-the collector 4-.with p conductivity to the neighboring base 3 and 12+ conductivity in the outer region 4a. The metallizing 6 on the emitter l is set back with respect to the control electrode 5. This measure provides the transverse-field emitter. The perforations 2a in the emitter zone 1 in the vicinity of the control electrode 5 are connected by a ring-shaped layer of metal 612 to the remaining metallizing 6 on the emitter l. The thickness of the layer 6b is made such, regard being had to the specific resistance of the material used, that on the one hand the base regions 2a which it covers are short circuited to -the neighboring emitter regions 1, and on the other hand there circuited emitter exhibits stable temperature behavior, since the inverse currents which increase with rising temperature flow away via the metallizing, and cannot lead to premature firing-Semiconductor elements of the type described above tolerate-relatively rapid increases in voltage without the occurrence of undesired firing through (see German Pat. specification NO. 1,154,872, open to public inspection).

If a semiconductor element is required to'be usable, with very rapid increases in voltage, the clearances between the in dividual emitter short circuits and between the emitter short circuits and the control electrode must be small. In the case of semiconductor elements which are required to be usable simultaneously for rapid increases in voltage and rapid increases in current, the first few emitter short'circuits in the vicinity of the control electrode must be disposed in a region to which no contact should be made, so that a voltage drop which is sufficient for firing to spread rapidly is set up across the noncontacted region of the emitter in the vicinity of the control electrode.

vAccordingly, it has hitherto also been impossible, in the case of a semiconductor element with a transverse-field emitter, to design the short-circuited emitter so that the semiconductor element may be expected to tolerate very rapid increases in voltage without the occurrence of undesired firing-through.

The present invention stems from the problem of developing such a semiconductor element. According to the invention, a semiconductor element of the type described at the beginning, which has to solve the aforementioned problem, it so designed that perforations disposed in the region in the vicinity of the control electrode are connected in electrically conductive fashion to the remaining metallizing in such a manner that, on the one hand, the inner zone is short circuited to the outer zone, and that on the other hand, when anode current flows after firing, a voltage drop which is sufficient for firing to spread rapidly is set up in a radially outward direction at least regionally across the region of the outer zone not covered by the metallizing.

is no interference with the development across the emitter region covered by the said layer 6b of a voltage drop which is sufficient for firing to spread rapidly.

.More particularly, the thickness of the metallic ring-shaped electrode portion 6b amounts to from about 5 to 10 microns corresponding to 20 to 40X l 0 whereas the thickness of the relativelythicker electrode portion 6 amounts to from about 50 to 100 microns, corresponding to 200 to 400X-10 which is a ratioof from about 1:10. Only the thicker metallic electrode part6, which ismade-of Ni, Au,.Al or Ta or alloys, is nickel plated and forms a further emitter contact.

Such a small thickness of the innerring-shaped electrode portion 612' from about 5 to 10 microns in contrast to the adjacent relatively thicker electrode layer 6 thus establishes the desired short circuit of the base regions 2a to the neighboring regions in the emitter l and also, due to its much higher resistance relative to that of the electrode portion 6, develops a voltage drop across it, i.e., the electrode portion 6b, which is sufficient for the firing to spread rapidly.

We claim:

1. In a semiconductor device, the combination comprising a wafer of semiconductor material divided transversely into four zones which alternate in polarity, one of the outer zones occupying a part of the adjacent front face of the semiconductor wafer, the remaining part of said front face bounding the neighboring inner zone, said outer zone constituting a transverse field emitter and having distributed therein a plurality of perforations and in which said neighboring inner zone extends as far as said adjacent front face, a control electrode applied on said front face to said neighboring inner zone, a metallizing layer having a thickness from about 50 to 109 microns covering a part of said outer zone such that another part of said 5 ing layer, said ring-shaped metallic layer having a thickness from about 5 to microns whereby the portions of said inner zone at said perforations which-it covers are short circuited to the neighboring outer zone but without interfering with the development across the part of said outer zone covered by said metallic layer of a voltagedrop sufficient for firing to 5 spread rapidly. 

1. In a semiconductor device, the combination comprising a wafer of semiconductor material divided transversely into four zones which alternate in polarity, one of the outer zones occupying a part of the adjacent front face of the semiconductor wafer, the remaining part of said front face bounding the neighboring inner zone, said outer zone constituting a transverse field emitter and having distributed therein a plurality of perforations and in which said neighboring inner zone extends as far as said adjacent front face, a control electrode applied on said front face to said neighboring inner zone, a metallizing layer having a thickness from about 50 to 100 microns covering a part of said outer zone such that another part of said outer zone neighboring said control electrode and provided with circumferentially spaced perforations surrounding said control electrode remains free from said metallizing layer, and a ring-shaped metallic layer connecting said perforations in the region neighboring said control electrode to said metallizing layer, said ring-shaped metallic layer having a thickness from about 5 to 10 microns whereby the portions of said inner zone at said perforations which it covers are short circuited to the neighboring outer zone but without interfering with the development across the part of said outer zone covered by said metallic layer of a voltage drop sufficient for firing to spread rapidly. 